In the past, engine oil has been used to lubricate and cool an internal combustion engine (below, also referred to as an “engine”). For example, the engine oil is stored in an oil pan provided under the engine and is fed to the different parts of the engine by an oil pump. The engine oil circulated through the engine parts contains foreign matter such as impurities. In general, to remove this foreign matter, an oil filter has been provided in the oil path into which the engine oil flows.
As such an oil filter, a spin-on type or cartridge type oil filter comprising a filter member made of a filter paper etc., housed in a casing is generally known. The filter member generally has a pore size of about 18 μm. Therefore, in a conventional oil filter, while it was possible to remove relatively large foreign matter, for example, foreign matter such as abrasion dust, there was the problem that smaller foreign matter, for example, foreign matter such as soot ingredients (burned hydrocarbons and oxide products) or sludge ingredients could not be sufficiently removed. Such foreign matter led to deterioration of the oil and in turn sometimes had various detrimental effects on the different engine parts.
Patent Document 1 describes a filtration medium for filtering a lubricant oil comprising a thermally bonded sheet, the sheet comprising (a) about 1 to 40 wt % of a bicomponent binder fiber having a fiber diameter of about 5 to 15 micrometers and a fiber length of about 0.1 to 15 cm; and (b) about 60 to 99 wt % of a glass fiber having a fiber diameter of about 0.1 to 5 micrometers and an aspect ratio of about 10 to 10,000; wherein the media has a thickness of about 0.2 to 2 mm, a solidity of about 2 to 10%, a basis weight of about 10 to 50 g-m−2, a pore size of about 0.5 to 10 micrometers and a permeability of about 0.03 to 9.1 m-min−1 (0.1 to 30 ft-min−1).
In technical fields different from the above oil filter for an internal combustion engine, for example, various filtration membranes and production methods thereof have been proposed as described below.
Patent Document 2 describes a hollow-fiber porous membrane of vinylidene fluoride resin, comprising a porous membrane of vinylidene fluoride resin in a hollow-fiber form; and having a ratio Pmax/Pm of at most 2.0 between a maximum pore size Pmax and an average pore size Pm, and a Pm of 0.13 μm-0.25 μm, according to the half-dry/bubble point method (ASTM F316 and ASTM E1294); a coefficient of variation in outer surface pore size of at most 70%, and a porosity of 75-90%. Further, Patent Document 2 describes that such a hollow-fiber porous membrane of vinylidene fluoride resin shows excellent water-permeability maintenance power in continuous filtration of cloudy water.
Patent Document 3 describes a method of producing a multilayered structure ceramic filter comprising continuously depositing a slurry for forming different layers of a first layer to an n-th layer on the surface of a porous substrate by a cross-flow filtration method, drying the porous substrate after depositing the slurry for forming the different layers of the first layer to the n-th layer, and firing the dried porous substrate.